Method of and apparatus for air liquefaction



Spt. 9, 1930.

METHOD OF l uvam'oa Patented Sept. 9, 1930 UNITED STATES PATENT? OFFICE ISAAC H. LEVIN, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR, BY JYITESN'IIE'. ASSIGN- MENTS, TO GAS INDUSTRIES COMPANY,

roR'A'rm or PENNSYLVANIA OF PITTSBURGH, PENNSYLVANIA, A COR- METHOD OF AND APPARATUS FOR AIR LIQUE FACTION Application filed June 1,

The invention relates to method and appa ratus for the transfer of heat between fluids and the purification of fluids as is commonly required in the production of liquid air and related processes. In such processes, some of the constituents of the fluids during the heat transfer process may become congealed on the heat transfer surfaces. The fluid is .thus purified but the heat transfer may be ciently. Some of the specific objects con-' tributive to this end are herein mentioned.

The object of this invention is to enable one to build an interchanger of light weight and construction and thus minimize the loss of energy required to cool the mass of the inter-- changer.

Another object is to reduce the manufacturing cost of the apparatus.

A further object is to enable one to construct" an interchanger which shall require the simplest piping for interconnecting the interchanger with the rest of the apparatus. A further object is to enable one to operate an interchanger with the end that is at room temperature facing downward.

-A further object is to enable one to attain the above objectives and at the same time have an interchanger that will operate through long periods of time without clogging and thus avoid the necessity of frequent shut W1 downs and defrosting of the interchanger.

Another object is to build an interchanger with many paths in parallel instead of a few paths'in series. Another. object is to build an interchanger that will maintain its efliciency as measured by the difference in temperature between the incoming and outgoing fluids over long periods of operation.

The invention can be readily understood by referring to the accompanying drawing which embodies a device for carrying out the 1925. Serial No. 34,071.

same. A jacket 5 is fastened to tube sheets 1 placed at the top and bottom of the interchanger. Tubes 3 are fastened to the tube sheets. A head 2 is attached to top tube sheet and forms With it the space 15. A head 6 is attached to the bottom tube sheet and forms with it the space 13. The fluid may enter the interchanger at 8 pass thru distributor pipes 12 and then up the tubes 3 thru the nozzles. 4 and out thru the opening 9. Another fluid may enter opening 10 pass over the baflles'l i and then out thru the opening 11. N o specific method for fastening the jacket to the tube sheet or the tubes to the tube sheets are herein given as this will vary with the different fluids used and the temperature and pressure of same The nozzles 4 may be separate units distinct from the tubes but fastened to same or they may be formed by constrictions in the tubes depending upon the specific nature and condition-of the fluids handled.

The distributor 12 is here shown as a number of pipes spread out spider fashion from the inlet pipev 8. There are, however, many other means to distribute the fiui'd entering'8 so'that'the fluid may not be crowded up thru only some of the pipes 3. The specific device or scheme used to-obtain a distribution of the fluids thru the pipes 3 may likewise depend upon the specific conditions of the fluids treated.

The interchanger shows only two streamsin heat transfer relation, but the interchanger can be used to handle several streams (not shown) in similar relation to one another instead of the two streams herein described.

A good example of the application of this invention is to the production of oxygen by the air liquefaction process. Air under pressure is sent into tube 8 and is distributed in the space 13 and then passes up tubes 3, thru the nozzles 4 and into the space 15 and then thru outlet 9 into the fractionating column.

The air is treated in the column and separated into its constituents. The nitrogen and oxygen and the other gases leave the column at the very low temperatures.

For the sake of making clear the operations that take place in the interchanger let. us assume that only the nitrogen passes into the interchanger shown and that the oxygen passes in heat transfer relation with a portion of the air in still another interchanger. The cold nitrogen enters at 10 passes over the baffles 14 and leaves at 11. The air enters at the bottom of the interchanger at about room temperature and leaves the top of the interchanger at very low temperatures. The air is as a rule treated while under pressure before it enters the interchanger so that it is free from carbon dioxide and moisture to the extent that can be brought about by agents such as caustic soda or caustic potash.

The temperature of the air at the exit of the interchanger is sufficiently low to precipitate practically all of the water and carbon dioxide. The nitrogen as it passes downwardly thru the interchanger gradually becomes warmer so that it leaves at 11 at about the temperature of the incoming air.

As the air becomes progressively colder frost and carbon dioxide snow tend to deposit out and thus purify the air, while at the same time the heat transmission coeflicient becomes reduced and actually pipe blockage may occur if provisions are not taken to give to the ascending air large passages for the deposits to form. The deposits start at about A or so from the top of the interchanger and as more deposits form this cold region descends until it gets down to too low a point for efficient heat transfer; the difference in temperature between the nitrogen and the air increases and too much heat is lost, and the operation of the column ceases to function properly.

If an interchanger as described but without the nozzles 4 or the equivalent for same and without the distributor were to be used the interchanger would not function, that is, the stream of nitrogen would not heat trans- .fer with the stream of air and the temperature difference between the air and the nitrogen would very rapidly become greater and greater.

Prior to my invention it was well known in the art that an ordinary tubular interchanger would give the dire results just described. Reference to this phenomena is given for example in U. S. Patent 1,323,014 by G. Claude. The reason that results can not be obtained is that the air as it gets colder gets heavier and convection currents are set up resulting in the cold air dropping to the bottom or warm end of'the interchanger.

Eddy currents are set up and the temperature gradient from top to bottom of the interchanger can not be maintained and the interchanger ceases to function properly. While a lack of uniformity in the flow of air in the tubes 3 exaggerates the adverse operating conditions, nevertheless perfect distribution does not entirely eliminate the eddy currents.

On the other hand the eflect of the nozzles on the flow of the air in the tubes eliminates the eddy currents and permits the successful use of the interchanger. The use of the nozzles 4 permit the use of larger size tubes 3 than is required for heat transfer and without appreciable loss in the over all heat transmission coelficient. This extra room in the tubes permits the accumulation of frost over long periods of time without clogging and also permits a saving in chemicals in the preliminary purification of the air.

It can now easily be seen how by the use of the novel features described by this invention the various objects set forth can be obtained and how very efficient and economical construction and operation for heat transfer and purification of fluids can be attained.

The use of the invention is not limited to an interchanger in the position herein shown and described. While only one nozzle 4 per tube 3 is described, the invention is not limited to only one, as several may be used in series.

The use of the word nozzle is not to be construed to be limited to just a nozzle, but to cover any scheme that will cause an increase in the velocity of the fluid in a portion of the tube or increase the differential pressure across portions of the tube.

The application of the invention is not limited to the examples of the use herein described but can be applied in various other Ways to the art mentioned and to other arts where heat transfer is required.

I claim:

1. In a heat interchanger, fluid conducting tubes within the interchanger for the upward flow of fluids through the same, a restriction within each tube placed in sections of the tubes near the tops and beyond the entrance thereof to increase the pressure drops in said sections of the tubes, and means adjacent the reduced portions of the tubes for introducing a separately confined downwardly flowing fluid to the interchanger.

2. In a heat interchanger for air liquefaction, means for introducing air into the bottom thereof, a vertically extending air conducting member having means disposed near its upper end only for increasing the velocity of the air passing therethrough, said conductor member throughout its remaining portion having an unrestricted passage, and means adjacent the velocity increasing means for introducing a separately confined downwardly flowing fluid to the interchanger.

3. In a heat interchanger having an outer shell, a lower fluid receiving chamber, an upper fluid discharge chamber, fluid conducting tubes in communication with the lower and upper chambers, means for increasing the velocity of the fluid while it is passing through the upper portions of the tubes, said means disposed beyond the entrance ends of the tubes and in proximity with the upper chamber, means disposed adjacent to the velocity increasing means for introducing a tubes.

separately confined cooling fluid to the interchanger, and means forpassing the cooling fluid through the interchanger in an opposite direction from the fluid 'passing'through the 4. The method of transferring heat between fluids and the products resulting from the fractional distillation of same, which consist in causing a plurality of parallel streams of a fluid to be passed in one direction and increasing the velocity of the fluidstreams at'the end of their passage to revent convection currents acting on the uid streams, and simultaneously passing a stream of a, product resulting from the fractional distillation in an opposite direction and in thermal contact with the saidfirst fluid streams, said introduction of said product being effectediat the point-of increased velocity.

5. The method of transferring heat between fluids and the products resulting from the fractional distillation of same, which consists in passing one fluid through a plu rality of parallel paths in an evenly distributed volume throughout the paths, increasing the velocity of the fluids in said paths at points near the termination thereof,

introducing'a' second fluid stream into thermal contact'with the first stream at points adjacent the said terminations, and simultaneously passing said second fiuid stream in an opposite direction and in thermal contact with said. first stream.

6. In an interchanger for air liquefaction having an outer shell, a relatively warm lower air admission chamber, a relatively cold upper discharge chamber, a series of vertically extending'flues arranged'in parallel connecting he saidchambers, restrictions in said flues located .near the upper chamber, an'dmeans for passing-a fluid downwardly, and in thermal contact with the upwardly passing air,

said latter means including a separately confined outershell fluid admission port disposed ad 'acent the said restrictions and at the upper en of the interchanger, a fluid discharge port at the lower end of the interchanger, and a series ofv baflles disposed-between the said ports. 7. In a heat interchanger, a fluid conduct- I tube located within the interchanger,

means associatedwith' the tube for effecting an upward flow of fluid through the tube, a restriction within the tube positioned near the top and beyond the entrance end thereof to increase the velocity of thefluid while it is passing through the upper portion of the tube, and means adjacent the reduced portion of the tube for introducing a separately confined downwardly flowing fluid to the inter:

' changer.

In testimony whereof I aflix my signature. 7

' ISAAC; H. LEVIN. 

